## Why
The skills extension needs the resolved turn environments to build a
real per-turn `SkillListQuery`. The previous `TurnLifecycleContributor`
hook only had a turn id, so it could only seed a placeholder query and
never carry the executor authorities that executor-scoped skill routing
will need.
Moving catalog resolution onto `TurnInputContributor` puts the skills
extension on the same turn-preparation path that already has the
environment ids and working directories for the submitted turn, while
keeping the actual prompt injection work for follow-up changes.
## What changed
- switch `ext/skills` from `TurnLifecycleContributor` to
`TurnInputContributor`
- build `executor_authorities` from `TurnInputContext.environments` and
pass them through `SkillListQuery`
- keep storing the resolved catalog in `SkillsTurnState`, but drop the
placeholder query helper that no longer matches the real data flow
- update the extension TODOs to reflect that per-turn catalog resolution
now happens in the turn-input contributor, and that prompt/context
injection still needs to move later
## Testing
- Not run locally.
## Why
`codex-core` currently owns the generic contextual-fragment trait and
several reusable fragment implementations. That makes it harder for
other crates to share the same host-owned model-input abstraction
without depending on all of `codex-core`.
This change extracts the reusable fragment machinery into a small
`codex-context-fragments` crate so future extension and skills work can
depend on the fragment abstraction directly.
## What Changed
- Added the `codex-context-fragments` crate with:
- `ContextualUserFragment`
- `FragmentRegistration` / `FragmentRegistrationProxy`
- additional-context fragment types
- Moved `SkillInstructions` into `codex-core-skills`, since
skill-specific rendering belongs with skills rather than generic core
context machinery.
- Kept `codex-core` re-exporting the fragment types it still uses
internally, so existing call sites keep the same shape.
- Updated Cargo and Bazel workspace metadata for the new crate.
## Verification
- `cargo metadata --locked --format-version 1 --no-deps`
- `just bazel-lock-update`
- `just bazel-lock-check`
jifandGitHub